Adding /opt/bin to PATH environment allows you to type python2.6 to start it.
In /opt/bin, "ln -sf python2.6 python" creates a symbolic link of python that links to python2.6 - combined with the above, now you should be able to just type python.
This applies to all user accounts.

Or you can create an alias of "alias python='/opt/bin/python2.6'", this is a per-user per-session option. You can automate it by adding the alias command in your shell start script (such as .profile or .bashrc, etc.)